San Francisco Giants' Buster Posey (28) swings for an RBI single off Oakland Athletics' Tommy Milone in the third inning of an exhibition spring training baseball game Thursday, March 28, 2013, in San Francisco.

Image 1 of 10 - Buster Posey's Spring Training

San Francisco Giants' Buster Posey (28) swings for an RBI single off Oakland Athletics' Tommy Milone in the third inning of an exhibition spring training baseball game Thursday, March 28, 2013, in San Francisco.

San Francisco Giants' Buster Posey (28) swings for an RBI single off...Oakland Athletics' Tommy Milone in the third inning of an exhibition...spring training baseball game Thursday, March 28, 2013, in San...Francisco.

Image 2 of 10|Buster Posey's Spring Training

Marcio Jose Sanchez / Associated Press

San Francisco Giants' Buster Posey during batting practice before an exhibition spring training baseball game against the Milwaukee Brewers on Wednesday, March 20, 2013 in Scottsdale, Ariz.

Image 2 of 10 - Buster Posey's Spring Training

San Francisco Giants' Buster Posey during batting practice before an exhibition spring training baseball game against the Milwaukee Brewers on Wednesday, March 20, 2013 in Scottsdale, Ariz.

San Francisco Giants' Buster Posey during batting practice before an...exhibition spring training baseball game against the Milwaukee Brewers...on Wednesday, March 20, 2013 in Scottsdale, Ariz.

Image 3 of 10|Buster Posey's Spring Training

Marcio Jose Sanchez / Associated Press

San Francisco Giants catcher Buster Posey (28) warms up before an exhibition spring training baseball game against the Arizona Diamondbacks on Sunday, March 3, 2013 in Scottsdale. Ariz.

Image 3 of 10 - Buster Posey's Spring Training

San Francisco Giants catcher Buster Posey (28) warms up before an exhibition spring training baseball game against the Arizona Diamondbacks on Sunday, March 3, 2013 in Scottsdale. Ariz.

San Francisco Giants catcher Buster Posey (28) warms up before an...exhibition spring training baseball game against the Arizona...Diamondbacks on Sunday, March 3, 2013 in Scottsdale. Ariz.

San Francisco Giants catcher Buster Posey, left, and shortstop Brandon Crawford wait in the dugout before an an exhibition spring training baseball game against the Seattle Mariners on Thursday, Feb. 28, 2013 in Scottsdale. Ariz.

Image 7 of 10 - Buster Posey's Spring Training

San Francisco Giants catcher Buster Posey, left, and shortstop Brandon Crawford wait in the dugout before an an exhibition spring training baseball game against the Seattle Mariners on Thursday, Feb. 28, 2013 in Scottsdale. Ariz.

San Francisco Giants catcher Buster Posey, left, and shortstop Brandon...Crawford wait in the dugout before an an exhibition spring training...baseball game against the Seattle Mariners on Thursday, Feb. 28, 2013...in Scottsdale. Ariz.

Image 8 of 10|Buster Posey's Spring Training

Marcio Jose Sanchez / Associated Press

San Francisco Giants' Buster Posey grimaces as he grounds out during the third inning of an exhibition spring training baseball game against the Colorado Rockies, Sunday, March 17, 2013, in Scottsdale, Ariz.

Image 8 of 10 - Buster Posey's Spring Training

San Francisco Giants' Buster Posey grimaces as he grounds out during the third inning of an exhibition spring training baseball game against the Colorado Rockies, Sunday, March 17, 2013, in Scottsdale, Ariz.

San Francisco Giants' Buster Posey grimaces as he grounds out during...the third inning of an exhibition spring training baseball game...against the Colorado Rockies, Sunday, March 17, 2013, in Scottsdale,...Ariz.

Image 9 of 10|Buster Posey's Spring Training

Marcio Jose Sanchez / Associated Press

San Francisco Giants catcher Buster Posey works out before an exhibition spring training baseball game against the Colorado Rockies on Thursday, March 21, 2013 in Scottsdale, Ariz.

Image 9 of 10 - Buster Posey's Spring Training

San Francisco Giants catcher Buster Posey works out before an exhibition spring training baseball game against the Colorado Rockies on Thursday, March 21, 2013 in Scottsdale, Ariz.

San Francisco Giants catcher Buster Posey works out before an...exhibition spring training baseball game against the Colorado Rockies...on Thursday, March 21, 2013 in Scottsdale, Ariz.

Image 10 of 10|Buster Posey's Spring Training

Michael Macor / The Chronicle

Giants' pitching coach Dave Righetti and catcher Buster Posey (28) meet on the mound with pitcher Scott Proctor, (51) as the San Francisco Giants play the Kansas City Royals in a Spring Training match up at Scottsdale Stadium on Saturday Mar. 9, 2013, in Scottsdale, Az.

Image 10 of 10 - Buster Posey's Spring Training

Giants' pitching coach Dave Righetti and catcher Buster Posey (28) meet on the mound with pitcher Scott Proctor, (51) as the San Francisco Giants play the Kansas City Royals in a Spring Training match up at Scottsdale Stadium on Saturday Mar. 9, 2013, in Scottsdale, Az.

Giants' pitching coach Dave Righetti and catcher Buster Posey (28)...meet on the mound with pitcher Scott Proctor, (51) as the San...Francisco Giants play the Kansas City Royals in a Spring Training...match up at Scottsdale Stadium on Saturday Mar. 9, 2013, in...Scottsdale, Az.

UPDATE, 12:00 P.M.: The Giants will announce Buster Posey’s eight-year, $161 million extension at today’s Play Ball lunch. It’s a $167 million contract that includes his $8 million already agreed to for 2013 and runs through 2021. It includes a $22 million option for 2022, raising the total potential value of his current deal to $186 million.

This is the largest contract in Giants history and the largest ever given to a catcher, though, of course, he won’t be a catcher for all of the deal.

It’s the second largest average annual value for a catcher. Joe Mauer’s is higher at $24 million. It’s also a record for the most money given to a player with less than three years of service time, more than doubling Carlos Gonzalez’s $80 million.

Here’s he breakdown of the money: $8 million this year, $12.5 million in ’14, $16.5 million in ’15, $20 million in ’16, then $21.4 million for each of the next five years covering five free-agency years. There’s a $3 million option buyout for 2022.

Buster has a full no-trade clause.

ORIGINAL POST: The Giants and 2012 NL Most Valuable Player Buster Posey have agreed on a long-term contract extension that will keep the catcher in San Francisco through 2021.

The deal includes a one-year option. Dollar figures were not immediately available.

The Giants and Posey reached a one-year, $8 million for 2013 during spring training.